Diplexing network



Jan. 30, 1951 O. M. WOODWARD, JR

DIPLEXING NETWORK Filed Dec. :@(1949 &mentor %ap/mea, E

aitomeg Patented Jan. 30, 1951 DIPLEXING NETWORK Oakley M. Woodward, Jr., Princeton, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application December 30, 1949, Serial No. 135,856

14 Claims.

This invention relates to radio frequency power networks wherein two independent sources, which must be electrically isolated from one another, are required to supply energy simultaneously to a common load device. 5 between the windings.

Diplexing networks, or networks for coupl'ng The novel features of the invention, as well as two sources of radio frequency energy without the invention itself, both as to its organization interaction, to a common load, such as an anand method of operation, Will best be understood tenna system, are known and find extensive apfrom the following description, when read in conplication in the art. One such system is dis-' nection with the accompanying drawings in closed and claimed in Patent No. 1454307, issued which: to G. H. Brown on November 30, 1948, for "Radio Figures 1 through 3 are schematic diagrams of Frequency Network. In an application filed three embodiments of my invention and October 4, 1948, for Radio Transmitters," Serial Figure 4 is a sectional View of a pair of radio No. 52,635, by G. H. Brown and assigned to a frequenc electrodes illustrative of one type of common assignee, there is described and claimed load which may be used with the embodiments of a coaxial line bridge cilrcuit which is used as a my invention. diplexer. Referring to Figure 1, a radio frequency gen- The elements used in these types of diplexing erator ID generates a voltage Ea and is connected networks are all on the order of half wavelengths to a load |2 through a trifilar coil l4. The trifilar or quarter wavelengths at the frequency of opcoil ld is made to have an electrical length of one eration, At the higher frequencies, in View of the quarter wave length at the midband frequency of shorter wavelengths, these diplexing networks are operation of generator ID. Two of the trilar coil of a convenient size and may be readily handled. windings are connected to one side l I of the gen- But at frequencies on the order of 20-30 megaerator n. The third trifilar coil winding is concycles and lower, such diplexing networks benected to the other side of the generator. This come quite large and complex in View of the side is shown as connected to ground. The load greater wavelengths. They consequently become |2 may be a single load having three input terawkward to handle and occupy valuable space. minals IS, !8, 20 with terminal !8 being a center It is therefore an object of my present invention se tap terminal and the impedance of each half of to provide an improved diplexing network which the load being equal to R. The load !2 may also is more compact than diplcxers of the prior art. represent two equal unbalanced loads each of It is another object of my present invention to impedance R and each being joined to the other provide an improved diplexing network which is at one end at the terminal l8. The trifilar coil Simpler than diplexers of the prior art, winding connected to the ground side of the gen- These and further objects of my invention are erator ID is connected at its other end to the achieved by connecting two individual sources of terminal IB and to ground. The remaining two radio freouency energy to a load composed of two trifilar coil windings 'are respectively connected substantially equal impedance loads connected to terminals B and !8, it being immaterial which together or a single load having a center tap. The 40 of the two windings goes to terminal i& or [8. connections are made by means of coiled trans- Another radio frequency generator 22 which mission line elements which are bifilar wound generates a voltage Eb is connected to terminals and, or, trilar wound. connections are made so IS and 20 of the load by a bifilar coil 24. The that the current applied by one of the generators bifilar coil 24 is made to have an electrical length is out of phase across the load and the current of one quarter wave length at the midband freapplied by the other generator is in phase across quency of operation of generator 26. One side of the load. The generator supplying the out-ofthe generator 22 is grounded. The arrows in the phase load current is placed at a point of zero diagram indicate the direction of flow, at the load potential with reference to the generator supply- !2, of Currents Ia and lb from res wctive generaing the in phase Currents by means of the multitors !0 and 22. Energy from generator !0 is fed filar windings connecting each generator to the by the trifilar coil, acting as a three wire transload. The multifilar windings between the load mission line, to the load !2, so that the currents and the generator supplying the in phase crurrent Ia at terminals l6 and 29 are in phase. For this acts ase' radio irequency choke'to any currents conditionthe bifilar coil24 acts as a high imfrom theni phase current supply generaton Thus p daincechoke coilto these in ph se Currents both generators are effectively decoupled from one another. The term multifilar coil is used here to mean a coil having two or more windings which are wound so that there is no mutual inductance henoe no current flows in generator 22 from generator iS. Thus generator I@ is isolated from genci-ater 22.

The bifilar coil 2:3 serves the purpose, as in the prior art, to couple an unbalanced generator 22 to a balanced load l For this condition the current Il) from generator 22 is out of phase at terminals i& and'and side M of'generatop t j' is at zero potential. Hence, generator i& is' decoupled from generator 22.

The trifilar coil M acts as a quarter wave stub (at midband frequency) with the winding com nected to terminal !8 at ground potential. If' the impedance of each of the; load sections: is R,

the characteristic impedance of: the bifil'ar. ccil H 24, Zb, should be made /2R in order that the generator 22 see an impedance. equal to R. In.

order that the generator l see an impedance R when looking toward the load the characteristic impedance Zt of the tri'lar coil is made equal to Figure 2-` is a schematic di'agram of a second'. embodment of my invention using two trilar coils; The arrangement of' generator li trifil'ar coil' l l and load l2 is the same as is' shown in: Fi'gure 1' and need' not bevredescribed. A' trifilar coil26 couples generator 22 to= the load- 112. Two

gether at one end and then connected to terminal, IE, the generator 22- is: connected between the other end of these two windi ngs. Fhe third' winding= of the trifilar coi=l= 22 is connected hetween terminal 28: and' the; grounded side` of generator 22.

The effect of connecting trifilar coil 26, in the;

fashion described is to provide; the. same result as: is achieved' withbiar coil: 24. The current:

from generator 22'is out of phase at' terminal. lt and' 261 and accordingly generator 22 is decoupled from generator m. Also. trifi-lar coil 26 acts as high impedance radio. frequency choke to the' Currents fromgenerator* e. and', thusgenerators l-fl and 22 are isolated; Trifilar'coil 25 is made' to have an electrical length of one.` quarter wave length at the midband frequency oi generator 22'. I-ts: impedanee is made, equal to'` in order that generator: 22 seean impedance equal' to' R'.

Figure 3 is: a schematic diagram of another embodiment of my' invention' using; only bifilar The interconnections of the load !2, the

coils. bifilar coil Ed, and' the generator 22 are as, heretoforedescribed. Generator ta* is connected' to the load 52 bymeans; of: two bifilar coils 28 39:' each of which hasan impedance equal to /2R and an electrical length of' one quarter wave length at the frequency of operation. The generator lil is connected between the windings at one end of each of the bifilar -coils 28, til; The other ends of the windings of the bifil'ar coils 28', au: which are connect-ed` to point H on the: generator, are respectively connected to terminals. l'E and' 26 at the load. The remainng windings: of the bifilar coils are connected to terminal !8' and grounded'.

The connecti'ons of the bifilar coils 28, t) efiect'ively prod'uce the same results as the trifilar winding M conneotions shown in Figures 1 and' In phase Currents Ia areproduced at terminals !6 Point H is at zero potential With, reerence to the out of phase currents produced by generator 22 at terminals IB, 20 and therefore generator 22 is efiectively decoupled from generator U.

Any type of radio frequency load may be used as the load !2. A transmitting antenna array adjusted to be balanced and to provide three input terminals is a most common load for this type of diplexing network A television picture transmitter and a sound transmitter may both be fed into a double line antenna, such as a turnstile antenna, without interaction between the two transmitters. Where resistance stabilzation of an antenna array is desired, either of the generators, li 22 may be replaced by a refiection absorbing resistance. The diplexing system also may beused in a receiving system for isolating two receivers, substituted in place of the generators ID, 22 and fed by a common antenna. By substituting an absorbing resistor in place; of, one of the receivers, refiectons caused by' a. mismatched antenna may be eliminated., The. impedance values shown are thes preferred ones. However these are not to. be taken as` limting values since other, impedance ratiovalues of load generators and multifi-lar coils maybe used' in accordance with good impedancematching practicesand substantially the same results. may be; obtained as' with the recommended imoi the' trifilar coil' windings are connected to- I?? pedance ratlos.

In an application` by GeorgeH., Brown for an "Improvement in Radio Frequeney Heating` System," filed September 1, .19493 No'. 113,581and i assigned to a common assig nee it isshown that;

two; generators may be used to feed, a common; pair of: bar electrodes used in radio.- frequeney heating. I-f' onea generator applies in, phase; voltages at the ends of one of the bar electrodes: and:: the other generator. applies outof-phase 'ivoltages at: the same ends of' the same bar elec trode 'more uniform heating` is obta-ined: and more power along the bar electrode; Any of the& embodiments' of the present. invention, shown, herein. may be used to. isolatingly couple' two; R F; heating generators to a common pair of' bar electrodes* in accordance with the teachings" of the` application of: Brown.

Eigure 4` is a sectional view of' an' upper bar: electrode 32' and a lower bar electrode 34which may' be a bedplate, heating a di'electric load 36. Terminals !6. and 20 are approximately at the ends' of the upper bar electrode 32. Terminal l'8 maybe the lower bar electrod'e 34. Connections may be made to' the electrodes from the; generator using the multilar wound coils as above shown.

From the foregoingdescription, it will be readily apparent that I` haveprovided an improved diplexing system, which, in view of thez coiled elements used; is more compact and' simpler than systems of the prior art. Although I' have shown and described several embodiments" of my invention, it should be apparent that many' other embodiments are possible, all within' the' spirit and scope of' my inventi'on. Therefore', I desire that the foregoing description shall be taken as iilustrative and not as limiting,

What is'claimed'is:

1. A system for exctation from two sources, of radio' frequency energy without interaction comprising a load having three input terminals, one of which is a center tap terminal' for said' load, at least one-multifi'lar-winding'connected bez-s tween one of' said radio frequency energy sources and said threeinptterminalsand another:multi` mar winding connected between the other of said radio frequency energy sources and two of said input terminals exclusive of said center tap terminal, each of said multifilar windings being one quarter wavelength at the midband frequency of the radio frequency energy source to which it is connected.

2. The system recited in claim 1 where at least one multilar winding is a trifilar winding and said other multiiar winding is a bifilar winding.

3. The system recited in claim 1 where at least one multilar winding is a trifilarwinding and said other multilar winding is a trifilar wind- 4. The sys'temrrecited in claim l where at least one multiilar winding consists of a pair of bifilar windings and. saidother multifilar winding is a bifilar winding.

.5-.1 The system recited in claim 1 wherein said load comprises a pair of bar electrodes for radio frequency heating, one of said bar electrodes having said center tap terminal connected to it, the remaining two input terminals being positioned on each end of the other bar electrode.

6. An isolation network for radio frequencv power systems including a pair oi radio frequency loads each havinga first and second input terminal, said second input terminals being connected together, a bifilar winding one quarter wavelength long at the Operating frequency, one end of said bifilar winding serving as a radio frequency power input and each winding at the other end being respectively connected to said first input terminal of each load, and a trifilar winding one quarter wavelength long at the Operating frequency, one end of said trifilar winding serving as a radio frequency power input and each winding at the other end being respectively connected t each of said first terminals of said pair of loads and to said second terminals.

7. The system recited in claim 6 wherein the pedance of said bifilar coil is determined as and the impedance of the trifilar coil is determined as where Zb is the impedance of the bifilar coil and Zt is the impedance of the trifilar coil and Ris the impedance of one of said loads.

8. An isolation network for radio frequency power systems including a pair of radio frequency loads each having a first and a second input terminal, said second input terminals being connected together, first trifilar coil one quarter wavelength long at the desired Operating frequency, having one end as a radio frequency power input, and having each winding at the other end connected respectively to a first terminal of one of said loads, to a first terminal of the other of said loads, and to the connected second terminals, and a second trifilar coil one quarter wavelength long at the desired Operating frequency, having one end as a radio frequency power input, having two of said windings at the other end connected to said first terminal of one of said loads and having the third of said second trifilar coil windings at the other end connected to said first terminal of the other of said loads.

9. The system recited in claim`8 wherein the impedance of said first and second trifilar coils 's determined as R Zt:-

,v where Zt is the impedance of the trifilar coil, and Ris the impedance of one of said loads.

10. Anisolation network for radio frequency power systems including a pair of radio frequency loads each having a first and second input terminal, said second input terminals being con c nected together, a pair of bifilar coils, each one i quarter wavelength long at the operating frequency, one winding in each of said pair of bifilar coils being connected together at one end and to said second input terminals, the other winding of each of said pair of bifilar coils being respectively connected at said one end to each of said first input terminals, the other ends of said one of said pair of bifilar coils being connected to the other end of said other of said pair of bifilar coils to serve as a radio frequency power input terminal, and a third bifilar coil having each winding at one end being respectively connected to each of said first terminals, the other end of said third bifilar coil serving as a radio frequency power input terminal.

11. The system recited in claim 10 wherein the impedance of each of one of said pair of bifilar coils and said third bifilar coil is determined as where Zb is the impedance of said bifilar coil, and R is the impedance of one of said loads.

12. A system for excitation from two sources of v radio frequency energy without interaction comprising a radio frequency load having first second and third input terminals, said second input terminal being said load center tap terminal, a trifilar coil one quarter wavelength long at the Operating frequency, each of the windings at one end of said trifilar coil being connected to a respective one of said input terminals, one of said sources of radio frequency energy being connected to the other end of said trifilar coil between the winding connected to said second terminal and the windings connected to said first and third terminals, and a bifilar coil one quarter wavelengthlong at the Operating frequency, said bifilar coil having the windings at one end connected to said first and third terminals and the other of said sources of radio frequency energy connected between the windings at said other end.

13. A system for excitation from two sources of radio frequency energy without interacton comprising a radio frequency load having first, second and third input terminals, said second input terminal being said load center tap terminal, a. first trifilar coil one quarter wavelength long at the Operating frequency, each of the windings at one end of said trifilar coil being connected to one of said input terminals, one of said sources of radio frequency energy being connected to the other end of said trifilar coil between the windin connected to said second input terminal and the other two windings, and a second trifilar coil one quarter wavelength long at the frequency of operation, said second trifilar winding having at one end two of its windings connected to said first terminal and its third winding connected to said ssa-,6512.

thirri; terminal, the. other* of sa-dsourcesof. radio frequency energy being connected to' the other. end of said second trifilar coil between one of said windings connected to said first terminal and the other two of said wi'ndngs.

14. A system for excitaton from two sources of radio frequency energy without interacton comprisng. a' radio frequency' load having first). second and thtd inputtermnals; said second; input terminal being said load center tap terminal; a' first bifila-r col one quarter` wavelength longa't' the operatngfrequency; one' end' of' said bin-lar coil' being' connected to* said` first' and third termiha'is; one of said radio frequency" sources being' connected' between the' other end of 'sad first bfilarcol and-a pair o-f bifilarcoifs each being one qarter wzwelength` long at* the frequency of operation, the windings` at* one end" of one of said' pair* of' bifla'r` coils being` connected to; said.. first and second' terminals, the; windngs atone end of the other of said pair of; bilar cols being' connected to said second and third: terminals, said other radio.` frequency energy source REFERENCES; CITED The*- following referenc'es are of record in: the fi1`eof this patent:

UNITED STATES PATENTS Number' Name: Dajt&

1139 055. Wright et al; Dec., 6; 1938? 2,341,120 Rudd et al. 4 Feb. 8; 1944 2-,341A08 Lindenblad Feb. 8,` 1944 

